1. Field of the Invention
The invention relates to a device for controlling the timing of grippers in a sheet delivery of a sheet-processing machine, in particular a sheet-fed printing machine, whereby the grippers release the entrained sheets at a predetermined location by controlled opening in dependence on various parameters, such as paper bond, sheet velocity, etc., and deliver the same to a sheet stack, and whereby the opening time or the opening position can be determined by shifting a landing body against which gripper opening means impinge which move with the grippers along a given travel path.
The invention is applicable in sheet-processing machines wherever sheets are transported by means of a transport device with grippers. The sheets are released from the grippers at a predetermined location for lowering on a sheet stack. The invention is particularly well suited in sheet-fed printing machines, in which the sheets transported by the sheet delivery are deposited on a sheet delivery table.
Chain deliveries are well known in printing machines. Gripper systems are evenly distributed about a continuous chain, usually two spaced-apart chains. The gripper systems grip a printed sheet arriving from the printing unit of the printing machine and then entrain and transport the same to the delivery table. At the delivery table, the grippers of the gripper system open up and release the sheet for deposit on the sheet stack. Various parameters define the exact time and/or location at which the grippers must be opened such that the sheet is properly released. Such parameters include the weight of the sheet, the printing speed and sheet velocity, the sheet format, etc. The opening time and location are predetermined.
A device of the foregoing type is known from German Patent 28 10 874, in which the grippers impinge on a landing body. The landing body actuates gripper opening means and the gripper releases the entrained sheets. The position of the landing body can be manually adjusted in dependence on the above-mentioned parameters. Printing speed is automatically taken into account, i.e. a change in the printing speed also causes a change in the position of the landing body. The landing body of the known device extends longitudinally in the travel direction of the grippers; it may be axially displaced and thereby brought into the desired position. The above-mentioned axial displacement of the landing body is effected by manually rotating a spindle. The spindle itself is axially shifted in dependence on the printing speed of the sheet-fed printing machine via a suitable mechanical assembly.
The known device must be built relatively long if an even opening behavior of the grippers is desired along the entire adjusting region of the landing body. Any shortening of the structure would bring about an undesirable shortening of the adjusting region or one would leave the straight-line region and move into the curved reversal region of the travel path. This would lead to inconsistent landing and roll-off angles of the gripper opening means on the landing body, as seen in comparison with other parts in the adjusting region. This, in turn, would lead to corresponding landing and roll-off shocks and thereby to great mechanical stresses and increased noise production. Also, it is not ensured that the grippers open up equally wide within the adjusting region, instead their opening width is uneven and in some regions unnecessarily large.